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L Ri <br /> • are included as Appendix B An tsoconcentration contour map of methyl- <br /> tertiary butyl ether (MTBE) concentrations is presented as Figure 3 <br /> 4.0 CONCLUSIONS <br /> • The groundwater samples collected from monitoring well MW-1 <br /> contained 43 ppb MTBE <br /> • The groundwater samples collected from monitoring well MW-2 <br /> contained 46 ppb MTBE, 21 ppb tert-butanol (TBA), and 93 ppb TPH-G <br /> • The groundwater samples collected from monitoring well MW-4 <br /> contained 50 ppb MTBE <br /> • The groundwater samples collected from monitoring well MW-5 <br /> contained 8 9 ppb MTBE, 21 ppb TBA, and 87 ppb TPH-G <br /> • No other hydrocarbons were detected above the laboratory method <br /> reporting limits in any of the groundwater samples collected <br /> The MTBE concentration in the groundwater sample collected from <br /> monitoring well MW-2 exceeded the California Department of Health <br /> Services (DHS) Maximum Contaminant Levels (MCLs) for drinking water <br /> No other compound concentrations exceeded MCLs Hydrocarbon and <br /> oxygenate concentrations decreased slightly in monitoring well MW-2, a n d <br /> the MTBE concentration in MW-1 remained very low for the fourth <br /> consecutive quarter The MTBE concentrations in monitoring wells MW-4 <br /> and MW-5 remained similar to last quarter No hydrocarbons were <br /> detected in groundwater samples collected from monitoring wells MW-3 <br /> and MW-6 <br /> 5.0 RECOMMENDATIONS <br /> ASE recommends continuing operation of the ozone sparging system a n d <br /> quarterly groundwater monitoring The next sampling is scheduled for <br /> April 2005 Since no significant hydrocarbon concentrations have been <br /> detected in upgradtent monitoring well MW-3 or the second-zone well <br /> MW-6 for over one year, ASE recommends removing these wells from the <br /> quarterly monitoring program <br /> • <br /> Singh's Unocal Service Station Quarterly Report -- January 2005 Sampling <br /> -3- <br />